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Historical 



It has been recognized since the dawn of microbiology that the 

 soil is inhabited by a living microscopic population which is respon- 

 sible for the numerous reactions that take place in the soil and that 

 affect the life and economy of man in many ways. Some of these 

 reactions brought about by the microorganisms in the soil are highly 

 beneficial, such as the destruction of various dead plant and animal 

 residues that find their way into the soil; other reactions are injurious 

 to plant and animal life, such as development of organisms which 

 serve as potential sources of many plant and animal diseases. Within 

 recent years, our knowledge of microbes in general and of soil mi- 

 crobes in particular, as they affect the cycle of life in nature, has 

 been greatly advanced to a point where the role of these organisms 

 in the transformation of matter and their importance in soil processes 

 and plant growth have been appreciated. 



Less than a century ago a battle was in progress among chemists, 

 plant physiologists, agronomists, and microbiologists. The contro- 

 versy centered about the role of microbes in the decomposition or 

 "fermentation" processes and in a number of other important reac- 

 tions that occur in nature, such as the effect of legumes on the 

 subsequent growth of cereals. 



The chemists, as typified by Justus von Liebig, as well as by 

 Berzelius and Wohler, maintained that the evolution of carbon 

 dioxide that takes place during the disintegration of sugars and 

 other organic materials was a purely chemical reaction, which was 

 described as "eremacausis." Liebig wrote: "All plants and vegetable 

 structures undergo two processes of decomposition after death. One 

 of these is named fermentation, the other decay, putrefaction, or 

 eremacausis. Decay is a slow process of combustion, a process, 

 therefore, in which the combustible parts of a plant unite with the 

 oxygen of the atmosphere." Berzelius believed that yeast was not a 



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